Congo red

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Congo red
Names
IUPAC name
Disodium 4-amino-3-[4-[4-(1-amino-4-sulfonato-naphthalen-2-yl)diazenylphenyl]phenyl]diazenyl-naphthalene-1-sulfonate
Other names
1-Naphthalene sulfonic acid 3,3'-(4,4'-biphenylenebis(azo))bis(4-amino) disodium salt
Benzidinediazobis- 1-naphtylamine-4-sulfonic acid disodium salt
C.I. Direct Red 28
Congo Red 4B
Congorot
Direct Red 28
Sodium diphenyldiazo-bis-a-naphthylaminesulfonate
Properties
C32H22N6O6S2Na2
Molar mass 696.665 g/mol
Appearance Red to red-brown solid
Melting point 360 °C (680 °F; 633 K)
Boiling point Decomposes
11.6 g/100 ml (20 °C)[1]
Solubility Soluble in ethanol
Almost insoluble in acetone
Insoluble in diethyl ether
Vapor pressure ~0 mmHg
Hazards
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
190 mg/kg (rat, IV)
Related compounds
Related compounds
Methyl red
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Congo red is an organic compound, an azo dye used in histology.

Properties

Chemical

Due to a color change from blue to red at pH 3.0–5.2, Congo red can be used as a pH indicator.

Physical

Congo red is a reddish or reddish-brown solid, soluble in water.

Availability

Congo red can be bought from chemical suppliers.

Preparation

Congo red can be synthesized by azo coupling of benzidine HCl and sodium napthionate.[2]

Projects

  • Azo dye
  • pH indicator
  • Histological stain
  • Detecting and estimating free HCl in gastric contents

Handling

Safety

Congo red is irritant and there is evidence to suggest it may cause cancer.

Storage

In closed bottles, away from light and air.

Disposal

Can be destroyed with a strong oxidizing solution.

References

  1. Solubility Handbook. - T.1, Book.1. - M.-L.: IAN USSR, 1961 (Справочник по растворимости. - Т.1, Кн.1. - М.-Л.: ИАН СССР, 1961)
  2. Shabir, Ghulam; Saeed, Aamer; Journal of the Chemical Society of Pakistan; vol. 39; nb. 1; (2017); p. 50 - 58

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